Semiconductor manufacturing processes utilize a wide variety of gases, such as fluorine-based gases, chlorine-based gases, silanes, oxygen, nitrogen, organic gases (such as hydrocarbons and fluorocarbons), and noble gases (such as argon or helium). In order to provide uniform distribution of processing gases into a semiconductor processing chamber (such as an etch chamber or a deposition chamber), a “showerhead” type gas distribution assembly has been adopted as a standard in the semiconductor manufacturing industry. Several current showerhead designs are summarized below.
U.S. Pat. No. 5,451,290, issued Sep. 19, 1995, to Salfelder, discloses a quartz gas distribution plate containing a number of gas inlet holes having cross-sectional areas sufficiently small to prevent plasma from being present in the gas inlet holes, to inhibit formation of polymer material and flaking of contamination particles therefrom. The gas inlet holes are formed on the surface of the quartz gas distribution plate directly over a wafer being processed. Alternatively, the gas inlet holes are formed in the quart plate to radially extend to the peripheral edge of the quartz plate, so that contamination particles are said to fall outside the bounds of a wafer beneath the quartz plate. (Abstract)
U.S. Pat. No. 5,614,026, issued Mar. 25, 1997, to Williams, discloses a showerhead designed to provide uniform distribution of process gas, where the showerhead includes a plurality of gas inlets for supplying process gas to a semiconductor substrate surface, and a plurality of gas outlets for removing gas and volatile byproducts produced as a result of reaction of the process gas with the substrate surface. Each gas inlet is concentrically positioned within a respective gas outlet. The showerhead is said to improve the utilization of process gas species at the substrate surface by providing gas flow in a direction perpendicular to the substrate surface and avoiding flow of the process gas or volatile byproducts laterally across the substrate surface. The showerhead is said to be useful for uniform stripping of a mask of organic material by direct contact of the incoming reactive gas with the substrate surface and immediate removal of the process gas and volatile byproducts through the concentrically arranged gas outlets. (Abstract)
U.S. Pat. No. 5,781,693, issued Jul. 14, 1998, to Ballance et al., discloses a showerhead for use with a lamp head in a thermal processing chamber. The lamp head includes a high intensity source which emits radiation that heats a substrate within the chamber. The showerhead includes a top window on a side of the showerhead that is adjacent to the lamp head; a bottom window on a side of the showerhead that is adjacent to the substrate during processing; and a gas supply inlet through which a gas is introduced into a space between the top and bottom windows, where the top and bottom windows are transparent to the radiation from the source in the lamp head, and where the bottom window includes a plurality of gas distribution holes through which gas is injected from the space between the top and bottom windows into the chamber. (Abstract)
U.S. Pat. No. 5,976,261, issued Nov. 2, 1999, to Moslehi et al., discloses a multi-zone gas injection apparatus which uses a gas injection plate with multiple injection zones to deliver multiple process gases into a chamber for deposition onto a workpiece (for example, a silicon wafer). The gas showerhead separates the multiple process gases in a manner that is said to avoid premixing of the gases, thereby minimizing gas-phase nucleation and particulate generation. The showerhead is said to allow real-time independent control over the gas flow rates in N channels to achieve deposition uniformity. (Abstract)
U.S. Pat. No. 6,050,506, issued Apr. 18, 2000, to Guo et al., discloses a showerhead used for dispensing gas over a wafer in chemical vapor deposition (CVD), especially for CVD of metals. The pattern of holes is tailored to compensate for thermal and other effects, in particular by increasing the density of holes toward the periphery of the wafer in three or more zones. Such a variable pattern is said to be particularly useful for liquid precursors that are atomized in a carrier gas, in which case a second perforated plate in back of the showerhead face can be elminated, thereby reducing the flow impedance and the required pressure of the liquid-entrained gas, which tends to deposit out at higher pressures. (Abstract)
U.S. Pat. No. 6,086,677, issued Jul. 11, 2000, to Umotoy et al., discloses a faceplate for a showerhead of a semiconductor wafer processing system having a plurality of gas passageways to provide a plurality of gases to the process region without commingling those gases before they reach the process region within a reaction chamber. The showerhead contains a faceplate and a gas distribution manifold assembly. The faceplate defines a plurality of first gas holes that carry a first gas from the manifold assembly through the faceplate to the process region, and a plurality of channels that couple a plurality of second gas holes to a plenum that is fed the second gas from the manifold assembly. (Abstract)
U.S. Pat. No. 6,182,603, issued Feb. 6, 2001, to Shang et al., discloses a surface-treated showerhead for use in a substrate processing chamber. The showerhead includes a surface treatment, such as a non-anodized aluminum outer layer, an electro-polished surface of bare aluminum, or a fluorine-based protective outer layer. The surface-treated showerhead is designed to improve the rate of removal of materials deposited on the interior surfaces of the chamber during cleaning, reduces contamination of substrates during processing, and provides more efficient use of the power source used for heating the substrate during processing. (Abstract)
U.S. Pat. No. 6,586,886, issued Jul. 1, 2003, to Katz et al., discloses a gas distribution plate electrode for a plasma reactor. The gas distribution plate includes a front plate in the chamber and a back plate on an external side of the front plate. The gas distribution plate comprises a gas manifold adjacent the back plate. The back and front plates are bonded together, forming an assembly. The assembly includes an array of holes through the front plate and communicating with the chamber, and at least one gas flow-controlling orifice through the back plate and communicating between the manifold and at least one of the holes. The orifice has a diameter which determines gas flow rate to the at least one hole. In addition, an array of baffles (pucks) is at least generally congruent with the array of holes and disposed within respective ones of the holes to define annular gas passages for gas flow through the front plate into the chamber. Each of the annular gas passages is non-aligned with the orifice. (Abstract)
A cross-sectional schematic of one prior art showerhead assembly is shown in FIG. 1A. The showerhead assembly 100 includes an electrode 104 and a gas distribution plate 102. FIG. 1B shows a top view of gas distribution plate 102. Numerous tiny through-holes 108 are machined in gas distribution plate 102, through which various processing gases flow into a semiconductor processing chamber (not shown). In order to prevent a plasma from igniting in the through-holes 108, the holes typically have a diameter of about 0.020 inch or less (more typically, about 0.010–0.015 inch). During semiconductor processing, polymeric contaminants (by-products of etch or deposition processes) build up on the surface 110 of gas distribution plate 102. These polymeric contaminants can flake off and contaminate a semiconductor substrate (not shown) within the processing chamber. Therefore, when these polymeric contaminants build up to a critical level (as determined by the semiconductor manufacturer), the showerhead must be cleaned, resulting in chamber downtime and loss of productivity.
Polymeric contaminants typically do not build up inside through-holes 108 during semiconductor processing, because of the process gases flowing through the holes 108 during etch or deposition processes. However, during a cleaning process, these polymeric contaminants can get pushed up into through-holes 108 and into the cavity 106 between gas distribution plate 102 and electrode 104 (shown in FIG. 1A). Like the through-holes 108, a portion of cavity 106 typically has a diameter of about 0.020 inch or less, in order to prevent a plasma from igniting in cavity 106. Once through-holes 108 and/or cavity 106 become filled with contaminants, they can be extremely difficult to clean, because of their small size.
It would therefore be desirable to provide a gas distribution showerhead assembly which could be easily cleaned, with minimal chamber downtime.